Rate control for a virtual diversity receiver

ABSTRACT

Devices and methods for determining transmission rates based on a virtual diversity receiver (VDR) scheme are disclosed. Performance is improved through determination of appropriate transmission rates, which are determined based on one or more signal to interference plus noise ratios (SINRs). The SINRs are calculated using virtual noise and channel coefficient values obtained as part of the VDR scheme. Utilizing an underlying pilot structure a user device may receive several sets of symbols. These symbols are then used to obtain both real and virtual channel noise power values and channel coefficients. These values and coefficients are then used to determine first and second SINR values indicative of one or more channels in the communication network. These SINR values may correlate to transmission rates (modulation order and/or coding rate). The SINRs may be sent to a base station, or the user device itself may determine one or more transmission rates.

TECHNICAL FIELD

The present invention relates generally to improving data transmissionon telecommunication networks, and more particularly, to a method anddevice for determining transmission rates based on a virtual diversityreceiver scheme in a telecommunication network.

BACKGROUND

3GPP Long Term Evolution (LTE) is a standard for mobile phone networktechnology. LTE is a set of enhancements to the Universal MobileTelecommunications System (UMTS), and is a technology for realizinghigh-speed packet-based communication that can reach high data rates onboth downlink and uplink channels. As illustrated in FIG. 1, LTEtransmissions are sent from base stations 102, such as Node Bs (NBs) andevolved Node Bs (eNBs) in a telecommunication network 106, to mobilestations 104 (e.g., user equipment (UE)). Examples of wireless UEcommunication devices include mobile telephones, personal digitalassistants, electronic readers, portable electronic tablets, personalcomputers, and laptop computers.

The LTE standard is primarily based on Orthogonal Frequency DivisionMultiplexing (OFDM) in the downlink, which splits the signal intomultiple parallel sub-carriers in frequency, and Single CarrierFrequency Domain Multiple Access (SC-FDMA) in the uplink. A transmittime interval (TTI) is the basic logical unit. A radio resource element(RE) is the smallest addressable location within a TTI, corresponding toa certain time location and a certain frequency location. For instance,as illustrated in FIG. 2, a sub-frame 200 comprised of REs may betransmitted in a TTI in accordance with the LTE standard, and mayconsists of sub-carriers 204 in the frequency domain. In the timedomain, the sub-frame may be divided into a number of OFDM (or SC-FDMA)symbols 208. An OFDM (or SC-FDMA) symbol 208 may include a cyclic prefix206. Thus, the unit of one sub-carrier and one symbol is a resource unitor element 202.

Wireless communication systems may be deployed in a number ofconfigurations, such as Multiple-Input, Multiple-Output (MIMO) radiosystems. An exemplary MIMO system including a base station 302, such asan eNB, and user equipment 304 is shown in FIG. 3. When a signal istransmitted by the eNB 302 in a downlink, i.e., the link carryingtransmissions from the eNB to the UE 304, a sub-frame may be transmittedfrom multiple antennas 306,308 and the signal may be received at a UE304, which has one or more antennas. The radio channel distorts thetransmitted signals from the multiple antenna ports. UE 304 may usereceiver-diversity signal processing schemes to improve performance.

In an LTE system, transmissions intended for a first user are oftenoverheard by a second, unintended user. The second user may utilizeoverheard data packets in various ways. For instance, “Completely StaleTransmitter Channel State Information is Still Very Useful,” by M.Maddah-Ali and D. Tse, Allerton Conference, 2010, describes a multi-userdownlink MIMO scheme with a mechanism for information exchange betweensingle antenna terminals, where the terminals feed back channel stateinformation (CSI) to the serving base station. The serving base stationexploits this CSI to broadcast an additional signal, which each terminaluses to create a virtual diversity receiver (VDR). This type ofinformation exchange may be referred to as “stale feedback,” since thechannel may have changed significantly by the time the base stationtransmits the extra signal. In this scheme, a mobile device thatreceives signals on only a single antenna may still take advantage ofsimple receive-diversity processing techniques. Similarly, “Multi-UserARQ,” by Peter Larsson and Nicklas Johansson, IEEE VTC Spring, 2006,which is incorporated by reference herein in its entirety, discusses anAutomated Repeat request (ARQ) control scheme that exploits the factthat users frequently overhear each other's information.

Other techniques utilize an explicit pilot structure that can beeffectively used to facilitate the estimation of channel parameters atthe receivers, including true channel taps, as well as estimations ofthe virtual channels created by the VDR scheme. However, the presentlyknow schemes do not address the number of information bits per TTI ortransmission rate that may be supported in a given scheme.

The implemented transmission rate for a given scheme is dependent onwhat information is available regarding the quality of transmissionsreceived at a user device. Two exemplary types or rate controlmechanisms are a “fast rate control” mechanism, based on instantaneouschannel conditions, and a “slow rate control” mechanism, based onaverage channel conditions. The two mechanisms may be best suited fordifferent scenarios. For instance, at low Doppler speeds, channelprediction is accurate, such that fast rate control would be preferable.However, at higher Doppler speeds, it may be preferable to implementslow rate control in order to avoid prediction errors and ensure thatthe selected rate matches the average channel state. A communicationsystem may also include additional mechanisms to improve robustness,such as an outer-loop control mechanism to adjust certain estimates ifprevious iterations result in a rate that is too high or too low. Forinstance, outer-loop control may be based on monitoring the number ofHARQ transmissions actually required compared to a target value.

In a fast rate control scenario, a user device (or the base station) mayuse the most recent channel estimate, H_(ij)[t], between a transmitantenna j and receive antenna i with a noise estimate, z_(i)[t], toderive a desired transmission rate for information transmitted betweenantennas i and j. For instance, letH _(j) [t]=[H _(1j) [t],H _(2j) [t]] ^(T)  (i)be the channel coefficient vector associated with transmit antenna j attime t, with each of the elements corresponding to one receive antenna.In equation (i), the superscript “T” represents the transpose of avector or matrix.

Using a linear minimum mean-square error (MMSE) receiver, thetransmission rate of the data stream from a first transmit antenna couldbe determined based on the signal to noise plus interference ratio(SINR)SINR₁ =P ₁ H ₁ ^(H) [t](P ₂ H ₂ [t]H ₂ ^(H) [t]+R _(z))⁻¹ H ₁ [t]  (ii)where the superscript “H” represents the conjugate transpose, P_(j) isthe transmit power from antenna j, or the power adjustment factor fortransmit antenna j, and R_(z) is the covariance of noise,z[t]=[z ₁ [t],z ₂ [t]] ^(T)  (iii),which can be estimated using reference symbols.

Similarly, the SINR of a data stream from a second transmit antenna canbe determined bySINR₂ =P ₂ H ₂ ^(H) [t](P ₁ H ₁ [t]H ₁ ^(H) [t]+R _(z))⁻¹ H ₂ [t]  (iv).If a successive interference cancellation (SIC) receiver is used, thedata stream from one transmit antenna is detected and cancelled beforedetecting the other data stream. The order of detection may be fixed, ormay be based on some additional criterion. Without loss of generality,we describe the case where the data stream from the first antenna isdetected and canceled first. Then SINR₁ is unchanged, and SINR₂ may beestimated instead using:SINR₂ =P ₂ H ₂ ^(H) [t]R _(z) ⁻¹ H ₂ [t]  (v)The case where the stream from the second antenna is detected andcancelled first is handled similarly. Regardless of receiver type, SINR₁and SINR₂ may be translated into transmission rates using a look-uptable, for example, as shown in FIG. 8. In this particular example,transmission rate is determined based on the combination of modulationand coding rate, together.

In a situation where instantaneous or recently updated channelcoefficients are not available or reliable, slow rate control may beused because it is based on longer-term statistics. For instance, areceiver may estimate the power of one or more channel taps, using atime average, determined by

$\begin{matrix}{P_{H_{ij}{\lbrack t\rbrack}} = {\frac{1}{K}{\sum\limits_{k = 0}^{K - 1}{{H_{ij}\left\lbrack {t - D - k} \right\rbrack}}^{2}}}} & ({vi})\end{matrix}$where D is delay, and K is a number of values. Similarly, a noise powerestimate may be determined by

$\begin{matrix}{P_{z_{i}{\lbrack t\rbrack}} = {\frac{1}{K}{\sum\limits_{k = 0}^{K - 1}{{z_{i}\left\lbrack {t - D - k} \right\rbrack}}^{2}}}} & ({vii})\end{matrix}$for the same or different values of D and K. Alternative averagingmethods may be suitable as well. Assuming that the power estimates areavailable to a MMSE receiver, the SINR of a data stream from the firsttransmit antenna would be determined by

$\begin{matrix}{{SINR}_{1} = {\frac{P_{1}P_{H_{11}{\lbrack t\rbrack}}}{{P_{2}P_{H_{12}{\lbrack t\rbrack}}} + {P_{z - 1}\lbrack t\rbrack}} + \frac{P_{1}P_{H_{21}{\lbrack t\rbrack}}}{{P_{2}P_{H_{22}{\lbrack t\rbrack}}} + P_{z_{2}{\lbrack t\rbrack}}}}} & ({viii})\end{matrix}$and the SINR of a data stream from the second transmit antenna would bedetermined by

$\begin{matrix}{{SINR}_{2} = {\frac{P_{2}P_{H_{12}{\lbrack t\rbrack}}}{{P_{1}P_{H_{11}{\lbrack t\rbrack}}} + P_{z_{1}{\lbrack t\rbrack}}} + {\frac{P_{2}P_{H_{22}{\lbrack t\rbrack}}}{{P_{1}P_{H_{21}{\lbrack t\rbrack}}} + P_{z_{2}{\lbrack t\rbrack}}}.}}} & ({ix})\end{matrix}$If the receiver were a SIC receiver, and the first stream is detectedand cancelled first, then SINR₁ would be unchanged, and SINR₂ wouldbecome:

$\begin{matrix}{{SINR}_{2} = {\frac{P_{2}P_{H_{12}{\lbrack t\rbrack}}}{P_{z_{1}{\lbrack t\rbrack}}} + {\frac{P_{2}P_{H_{22}{\lbrack t\rbrack}}}{P_{z_{2}{\lbrack t\rbrack}}}.}}} & (x)\end{matrix}$The case where the second stream is detected and cancelled first ishandled similarly. Again, each SINR could be converted to a transmissionrate through the use of a look-up table.

Despite the foregoing, there remains a need for methods and systems fordetermining transmission rates based on virtual data in order to fullyrealize the improved transmission properties available in a virtualdiversity scheme. A stale feedback scenario, for instance as describedin Completely Stale Transmitter Channel State Information is Still VeryUseful, by M. Maddah-Ali and D. Tse, cannot be effectively utilizedwithout a rate control mechanism.

SUMMARY

Particular embodiments of the present invention are directed to devicesand methods for improving performance in a communication network thatincludes a plurality of transmit antennas and a plurality of userdevices.

Performance is improved through the determination of appropriatetransmission rates, which may be determined based on one or more signalto interference plus noise ratios (SINRs). The SINRs are calculatedusing virtual noise and channel coefficient values obtained as part of avirtual diversity receiver (VDR) scheme. For instance, utilizing asuitable pilot structure, such as the structure described herein orapplication Ser. No. 13/633,731, titled “Pilot Structure to Support aVirtual Diversity Receiver Scheme,” which is incorporated herein byreference in its entirety, a user device may receive several sets ofsymbols. These symbols are then used to obtain both real and virtualchannel noise power values and channel coefficients. These values andcoefficients are then used to determine first and second SINR valuesindicative of one or more channels in the communication network.According to certain aspects of the present invention, these SINR valuescorrelate to transmission rates (modulation order and/or coding rate).The SINRs may be sent to a base station for use in determiningtransmission rates or the user device itself may determine one or moretransmission rates and send the determined rate to one or more basestations. Accordingly, the additional information provided through theimplementation of a VDR scheme is fully utilized to improve performance.

In one particular aspect, a method for improving performance in acommunication network with a plurality of transmit antennas and userdevices is provided. The method includes receiving, at a first userdevice, a first set of received symbols, a second set of receivedsymbols, and a third set of received symbols. The method also includesobtaining a channel noise power value and a set of channel coefficients.The channel noise power value and the channel coefficients are based onthe first set of received symbols. The method also includes obtaining avirtual channel noise power value and a set of virtual channelcoefficients. The virtual channel noise power value and the virtualchannel coefficients are based on the second and third sets of receivedsymbols. The channel noise power value, the set of channel coefficients,the virtual channel noise power value, and the set of virtual channelcoefficients are each associated with one of the plurality of antennas.

First and second signal to interference plus noise ratios are thendetermined based on the obtained values and coefficients. The firstsignal to interference plus noise ratio is determined based on thechannel noise power value, the set of channel coefficients, the virtualchannel noise power value, and the set of virtual channel coefficients.The second signal to interference plus noise ratio is determined basedon at least one of the channel noise power value, the set of channelcoefficients, the virtual channel noise power value, and the set ofvirtual channel coefficients.

In certain aspects, the method further includes reporting the first andsecond signal to interference plus noise ratios to one or more basestations. The base station may use the reported signal to interferenceplus noise ratios to determine one or more transmission rates. Themethod may also include determining a transmission rate based on thefirst and second interference plus noise ratios at the user device, andsending the determined transmission rate to one or more base stations.

In another aspect, certain embodiments of the present invention aredirected to a mobile device operable in a communication network toreceive signals from a plurality of transmit antennas. The mobile deviceincludes a processor, a memory coupled to the processor, a transceivercoupled to the processor, and one or more antennas coupled to thetransceiver, which are configured to transmit and receive signals. Theprocessor is configured to receive a first set of received symbols, asecond set of received symbols, and a third set of received symbols. Theprocessor is further configured to obtain a channel noise power valueand a set of channel coefficients based on the first set of receivedsymbols, as well as a virtual channel noise power value and a set ofvirtual channel coefficients based on the second and third sets ofreceived symbols. The processor uses the channel noise power value, theset of channel coefficients, the virtual channel noise power value, andthe set of virtual channel coefficients to determine a first signal tointerference plus noise ratio. The processor also determines a secondsignal to interference plus noise ratio based on at least one of thechannel noise power value, the set of channel coefficients, the virtualchannel noise power value, and the set of virtual channel coefficients.The channel noise power value, the set of channel coefficients, thevirtual channel noise power value, and the set of virtual channelcoefficients are each associated with one of the plurality of transmitantennas.

According to certain embodiments, the processor is further configured toreport the first and second signal to interference plus noise ratios toone or more base stations. The processor may also be configured todetermine a transmission rate based on one or more of the first andsecond signal to interference plus noise ratios and transmit thetransmission rate to one or more base stations.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated herein and form partof the specification, illustrate various embodiments of the presentdisclosure and, together with the description, further serve to explainthe principles of the disclosure and to enable a person skilled in thepertinent art to make and use the embodiments disclosed herein. In thedrawings, like reference numbers indicate identical or functionallysimilar elements.

FIG. 1 is an illustration of a wireless communication system.

FIG. 2 is an exemplary sub-frame of an LTE transmission.

FIG. 3 is a block diagram of an exemplary MIMO system.

FIG. 4 is an illustration of a wireless communication system inaccordance with exemplary embodiments of the present invention.

FIG. 5 is a block diagram of a user device in accordance with exemplaryembodiments of the present invention.

FIG. 6 is an illustration of pilot sequences in accordance withexemplary embodiments of the present invention.

FIG. 7 is a flow chart illustrating a process for improving performancein a communication network in accordance with exemplary embodiments ofthe present invention.

FIG. 8 is a table relating SINR to modulation order and coding rate.

FIG. 9 is a flow chart illustrating a process for improving performancein a communication network in accordance with exemplary embodiments ofthe present invention.

FIG. 10 is an illustration of a wireless communication system inaccordance with exemplary embodiments of the present invention.

FIG. 11 is an illustration of a wireless communication system inaccordance with exemplary embodiments of the present invention.

DETAILED DESCRIPTION

Particular embodiments of the present invention are directed to devicesand methods for determining transmission rates for a virtual diversityreceiver (VDR) based on one or more signal to interference plus noiseratios (SINRs).

In order to improve the performance of a communication network, a VDRscheme may be implemented to exchange information between user devicesvia an intermediary device, such as a base station, as shown for examplein FIG. 4. A pilot structure supports estimation of channel parametersat the receivers, including true channel taps, as well as estimations ofthe virtual channels created by the VDR scheme. Accordingly, eachterminal performs as if it has more receive antennas than it actuallydoes, which enables the use of receive-diversity signal processingtechniques.

FIG. 5 illustrates a block diagram of an exemplary UE communicationdevice 404. As shown in FIG. 5, the UE communication device may include:a plurality of transmit antennas 502, a data processing system 506,which may include one or more microprocessors and/or one or morecircuits, such as an application specific integrated circuit (ASIC),field-programmable gate arrays (FPGAs), or the like, and a data storageor memory system 508, which may include one or more non-volatile storagedevices and/or one or more volatile storage devices (e.g., random accessmemory (RAM)). The one or more antennas 502 are connected to transceiver504, which is configured to transmit and receive signals via theantennas 502.

In embodiments where data processing system 506 includes amicroprocessor, computer readable program code may be stored in acomputer readable medium, such as, but not limited to, magnetic media(e.g., a hard disk), optical media (e.g., a DVD), memory devices (e.g.,random access memory), and the like. In some embodiments, computerreadable program code is configured such that when executed by aprocessor, the code causes the data processing system 506 to performsteps described below (e.g., steps described below with reference to theflow charts shown in FIG. 7). In other embodiments, the UE communicationdevice 404 is configured to perform steps described above without theneed for code. That is, for example, data processing system 506 mayconsist of one or more ASICs. Hence, the features of the presentinvention described above may be implemented in hardware and/orsoftware. For example, in particular embodiments, the functionalcomponents of the UE communication device 504 described above may beimplemented by data processing system 506 executing computerinstructions, by data processing system 506 operating independent of anycomputer instructions, or by any suitable combination of hardware and/orsoftware.

According to certain embodiments, the methods and systems of the presentinvention may be implemented in a communication network that includes abase station with multiple transmit antennas, while a number of userdevices in communication with the base station have only a singlereceive antenna. One of ordinary skill in the art will recognize thatthis scenario may be extended to the case of K transmit antennas and Kuser devices, for K>2. Similarly, the processes disclosed herein mayalso apply to user devices that have more than one receive antenna.

For example, as illustrated in FIG. 4, a base station 402 having atleast two transmit antennas transmits information to two user devices,404,406. The user devices 404,406 have a single receive antenna and cancommunicate with the base station 402 via one or more communicationchannels. However, they cannot communicate with each other.

The base station 402 transmits a first plurality of information symbols,u[t], intended for a first of the user devices 404. For instance, at afirst time, t=1, base station 402 transmits two sets of informationsymbols, u₁[1] and u₂[1], which are intended for the first terminal,user device 404. (Here and in the description below, boldfaced variablesindicate vectors representing a set of symbols.) The first set ofinformation symbols, u₁[1], may be transmitted from a first transmitantenna of the base station 402, while the second set of informationsymbols, u₂[1], may be transmitted from a second transmit antenna of thebase station 402. These signals are not only received by the intendeduser device, 404, but also by a second terminal, user device 406. Eachset of information symbols, u_(j)[t], include a set of data symbols anda set of pilot symbols. A set of pilot symbols forms a pilot sequence.Thus, the sequence formed by the pilot symbols within the first set ofinformation symbols is referred to as the first pilot sequence and thesequence formed by the pilot symbols within the second set ofinformation symbols is referred to as the second pilot sequence. Thefirst and second sequences within the first plurality of informationsymbols are together referred to as the first plurality of pilotsequences.

Similarly, at t=2, the base station 402 transmits a second plurality ofinformation symbols including two sets of information symbols, u₁[2] andu₂[2], which are intended for the second terminal, user device 406. Thistransmission will be overheard by the unintended recipient, user device404. Each set of information symbols include a set of data symbols and aset of pilot symbols. Thus, the sequence formed by the pilot symbolswithin the first set of information symbols is referred to as the firstpilot sequence and the sequence formed by the pilot symbols within thesecond set of information symbols is referred to as the second pilotsequence. The first and second sequences within the second plurality ofinformation symbols are together referred to as the second plurality ofpilot sequences.

The resulting system is given byr ₁ [t]=H ₁₁ [t]u ₁ [t]+H ₁₂ [t]u ₂ [t]+z ₁ [t]  (1)for i=1, 2, where u₁[t] denotes the set of information symbolstransmitted from antenna j, H_(ij)[t] denotes the channel from transmitantenna j to terminal i, r₁[t] denotes the set of received symbols atterminal i, and z₁[t] denotes the noise at terminal i.

The term symbol may be understood in the present context asrepresentative of either a single symbol in a particular RE or as ablock of multiple symbols, such as in the time, frequency, or codedomains, or any combination thereof. In order to facilitate channelestimation, a pilot symbol structure is incorporated into theinformation symbols of the transmitted signal. The pilot symbols shouldbe known to the receiving user devices. This pilot structure complementsa stale feedback scheme and enables the estimation of both true andvirtual channel taps. Exemplary pilot sequences are shown in FIG. 6.

According to certain embodiments of the present invention, the set ofinformation symbols u₁[t] is comprised of N individual symbols,occupying N resource units. Those resource units may be distributed intime, frequency or code space, and may be contiguous or spread out.Independent of how the symbols are placed physically, without any lossof generality, one may consider u₁[t] as a 1-dimensional sequence oflength N, with elements u_(j,k)[t], k=1 . . . N.

According to certain embodiments of the present invention, the set ofinformation symbols u₁[t] is comprised of N_(d) data symbols, denoted byd₁[t], and N_(p)=N−N_(d) pilot symbols, denoted by p₁[t]. A set of pilotsymbols p₁[t] may occupy a first portion of u₁[t], e.g., the first N_(p)resource units of u₁[t]. A set of data symbols d₁[t] may occupy the lastN_(d) resource units of u₁[t]. This configuration may be defined by thefollowing:p _(j,k) [t]=u _(j,k) [t],k=1 . . . N _(p)  (2)andd _(j,k) [t]=u _(j,k+N) _(p) [t],k=1 . . . N _(d)  (3)

Pilot symbols may be strategically placed within a given transmission inorder to facilitate certain aspects of channel estimation. For instance,In an OFDM system, pilot symbols may be spread out in time andfrequency, to capture frequency variations. Alternatively, in a GSMsystem, they may be lumped together in the middle of a time slot tocapture time dispersion.

In certain aspects, the pilot symbols of two pilot sequences p₁[t], andp₂[t], are placed in the same air interface resource units. Accordingly,they will overlap completely at the receiver. In addition, the two pilotsequences may be chosen to be orthogonal to each other, i.e., that theinner product between the pilot sequences is zero:

$\begin{matrix}{{\sum\limits_{k = 1}^{N_{p}}{{p_{1,k}\lbrack t\rbrack}{p_{2,k}^{*}\lbrack t\rbrack}}} = 0} & (4)\end{matrix}$This orthogonality property may improve channel estimation at thereceivers, user devices 404 and 406.

A received signal r₁[t] at terminal i may be given by equation (1), withelements r_(i,k)[t], k=1 . . . N. According to an embodiment, the firstN_(p) symbols correspond to pilot symbol locations. A terminal, forinstance user devices 404 and 406, can compute the estimate

$\begin{matrix}{{{\hat{H}}_{ij}\lbrack t\rbrack} = {\sum\limits_{k = 1}^{N_{p}}{{r_{i,k}\lbrack t\rbrack}{p_{j,k}^{*}\lbrack t\rbrack}}}} & (5)\end{matrix}$which may be scaled by Σ_(k=1) ^(N) ^(p) p_(j,k)[t]p_(j,k)*[t]. Otherchannel estimation schemes may be used alternatively. For example, thecharacteristics of the impairment component in the received symbols maybe accounted for in the channel estimation process as in the case ofminimum mean-square error (MMSE), maximum-likelihood (ML), ormaximum-a-posteriori (MAP) channel estimation. Although Ĥ_(ij)[t] may bedistorted by noise, it is not distorted by the other channel's signal,in the case of pilot orthogonality. Also, N_(p) can be chosen largeenough to ensure that Ĥ_(ij)[t] is close to the desired H_(ij)[t]. Sucha selection reduces the number of data symbols N_(d) that may betransmitted.

According to an embodiment, each of the terminals, user devices 404 and406, communicate channel information to the base station 402 afterreceiving the information symbols discussed above. For example, userdevice 404 has received r₁[1], while user device 406 has received r₂[2],each containing the respective intended information symbols. Similarly,user device 404 has received r₁[2], while user device 406 has receivedr₂[1], each containing the respective unintended information symbols.

The base station 402 then receives feedback information from the userdevices 404,406. For instance, the base station 402 receives first andsecond channel estimates for a first transmission from the second userdevice 406, and the base station 402 also receives first and secondchannel estimates for a second transmission from the first user device404. According to certain embodiments of the present invention, eachterminal, i, feeds back the channel values H_(ij)[t] for t≠i. Thesevalues are received by the base station 402 before a third time, t=3.

Using the channel estimates, the base station 402 can synthesizereceived values {circumflex over (r)}₁[2] and {circumflex over (r)}₂[1]according to{circumflex over (r)} _(i) [t]=H _(i1) [t]u ₁ [t]+H _(i2) [t]u ₂[t]  (6)These values may be transmitted to the user devices 404 and 406 so thateach can recover the parts it needs in order to form a virtual antenna.

The base station 402 then determines one or more composite values basedon the channel estimates. For instance, the base station 402 may combinethe synthesized values according tou ₁[3]=r ₁[2]+r ₂[1]  (7)

The composite value, which includes one or more composite pilotsequences, is then transmitted from base station 402. It may betransmitted, for example, at t=3 from the first antenna. According tocertain embodiments of the invention, the second antenna may be silentduring transmission of the combined symbol.

The set of composite symbols u₁[3], described by equation (7) may beexpanded to yield

$\begin{matrix}\begin{matrix}{{u_{1}\lbrack 3\rbrack} = {{{\overset{\Cap}{r}}_{1}\lbrack 2\rbrack} + {{\overset{\Cap}{r}}_{2}\lbrack 1\rbrack}}} \\{= {{{H_{11}\lbrack 2\rbrack}{u_{1}\lbrack 2\rbrack}} + {{H_{12}\lbrack 2\rbrack}{u_{2}\lbrack 2\rbrack}} + {{H_{21}\lbrack 1\rbrack}{u_{1}\lbrack 1\rbrack}} + {{H_{22}\lbrack 1\rbrack}{u_{2}\lbrack 1\rbrack}}}}\end{matrix} & (8)\end{matrix}$where H_(ij)[t] is used in place of Ĥ_(ij)[t] to maintain consistency.According to certain embodiments of the present invention, the pilot anddata symbols within each set of the information symbols u_(j)[t], arethe same as in the original transmissions at t=1 and 2. In oneembodiment, the first N_(p) resource units of the set of compositesymbols are occupied by pilot symbols and form the pilot sequence p₁[3],where the kth symbol in the pilot sequencep _(1,k)[3]=H ₁₁[2]p _(1,k)[2]+H ₁₂[2]p _(2,k)[2]+H ₂₁[1]p _(1,k)[1]+H₂₂[1]p _(2,k)[1]  (9)for k=1 . . . N_(p). In this scheme, the pilot sequence itself is alinear combination of pilot sequences.

According to certain embodiments of the present invention, the firstuser device 404 receives the set of composite symbols at time t=3. Thereceived signal, r₁[3], may be defined asr ₁[3]=H ₁₁[3]u ₁[3]+z ₁[3]=H ₁₁[3]({circumflex over (r)}₁[2]+{circumflex over (r)} ₂[1])+z ₁[3]  (10)Because the expression of equation (10) includes {circumflex over(r)}₂[1], user device 404 can use r₁[3] to create a signal at a secondvirtual antenna, labeled 2, at time t=1, r₂ ^(v)[1]. This signal may beused to complement the true signal, r₁[1], of user device 404. Userdevice 404 received r₁[2] earlier; thus, it can use it to eliminate{circumflex over (r)}₁[2] from equation (10) to obtain the effectivesignal at virtual antenna 2, which is denoted r₂ ^(v)[1] and given by

$\begin{matrix}\begin{matrix}{{r_{2}^{v}\lbrack 1\rbrack} = {{r_{1}\lbrack 3\rbrack} - {{H_{11}\lbrack 3\rbrack}{r_{1}\lbrack 2\rbrack}}}} \\{= {{{H_{11}\lbrack 3\rbrack}{{\overset{\Cap}{r}}_{2}\lbrack 1\rbrack}} + {z_{1}\lbrack 3\rbrack} - {{H_{11}\lbrack 3\rbrack}{z_{1}\lbrack 2\rbrack}}}} \\{= {{{H_{11}\lbrack 3\rbrack}{H_{21}\lbrack 1\rbrack}{u_{1}\lbrack 1\rbrack}} + {{H_{11}\lbrack 3\rbrack}{H_{22}\lbrack 1\rbrack}{u_{2}\lbrack 1\rbrack}} + \left( {{z_{1}\lbrack 3\rbrack} - {{H_{11}\lbrack 3\rbrack}{z_{1}\lbrack 2\rbrack}}} \right)}} \\{= {{{H_{21}^{v}\lbrack 1\rbrack}{u_{1}\lbrack 1\rbrack}} + {{H_{22}^{v}\lbrack 1\rbrack}{u_{2}\lbrack 1\rbrack}} + {z_{2}^{v}\lbrack 1\rbrack}}}\end{matrix} & (11)\end{matrix}$whereH _(2j) ^(V)[1]=H ₁₁[3]H _(2j)[1]  (12)is the effective channel to virtual antenna 2, andz ₂ ^(V)[1]=z ₁[3]−H ₁₁[3]z ₁[2]  (13)is the effective noise at virtual antenna 2. Essentially, r₂ ^(v)[1]looks like a received signal at a virtual second antenna at user device404 at time t=1. The processing described in equations (11)-(13) may bereferred to as “VDR processing.”

Similarly, the second user device 406 can utilize u₁[3], because itcontains {circumflex over (r)}₁[2]. At time t=3, user device 406receivesr ₂[3]=H ₂₁[3]u ₁[3]+z ₂[3]=H ₂₁[3]({circumflex over (r)}₁[2]+{circumflex over (r)} ₂[1])+z ₂[3]  (14).The second user device 406 can then use r₂[3] to estimate a signal at asecond virtual antenna, labeled 1, at time t=2, to complement its truesignal r₂[2]. User device 406 eliminates {circumflex over (r)}₂[1] fromr₂[3] to obtain its own signal from virtual antenna 1 at time t=2, givenby

$\begin{matrix}\begin{matrix}{{r_{1}^{v}\lbrack 2\rbrack} = {{r_{2}\lbrack 3\rbrack} - {{H_{21}\lbrack 3\rbrack}{r_{2}\lbrack 1\rbrack}}}} \\{= {{{H_{11}^{v}\lbrack 2\rbrack}{u_{1}\lbrack 2\rbrack}} + {{H_{12}^{v}\lbrack 2\rbrack}{u_{2}\lbrack 2\rbrack}} + {z_{1}^{v}\lbrack 2\rbrack}}}\end{matrix} & (15)\end{matrix}$whereH _(1j) ^(V)[2]=H ₂₁[3]H _(1j)[2]  (16)is the effective channel to virtual antenna 1, andz ₁ ^(V)[2]=z ₂[3]−H ₂₁[3]z ₂[1]  (17)is the effective noise at virtual antenna 1.

Overall, the above-described scheme requires 3 channel uses to transmit4 information symbols. The total rate is R=4/3 symbols per channel use.Because each user device feeds back information to the base station, thebase station can exploit the multi-user nature of the scenario toefficiently pack information for more than one terminal in subsequenttransmissions, e.g., composite symbols, and minimize the number of timeperiods. According to the above-described scheme, a VDR transmissioncycle comprises of transmissions at t=1, 2, and 3. The VDR transmissioncycle is repeated subsequently. For simplicity, we refer to the 3 phasesin the cycle as t=1, 2 and 3. That is, the sequence of transmissionsfollows the pattern 1, 2, 3, 1, 2, 3 . . . .

According to particular embodiments of the present invention, a basestation, such as base station 402, includes one or more antennas, one ormore transceivers, and data processing resources, which together areconfigured to implement the pilot structure and VDR communication schemedetailed above. The pilot structure and VDR communication schemedescribed herein may also require certain actions and determinations bythe user device 404.

In certain embodiments, a user device, for instance, user device 404,receives a first plurality of received symbols. These received symbolsinclude a first set of data symbols and a first plurality of pilotsequences. For instance, the received symbols may include pilotsequences p₁[1] and p₁[2] shown in FIG. 6. They may be received from abase station, such as base station 402.

User device 404 then receives a second plurality of received symbols.These received symbols include a second set of data symbols and a secondplurality of pilot sequences. For instance, the second plurality ofinformation symbols may include pilot sequences p₁[2] and p₂[2] shown inFIG. 6. According to particular embodiments, the first plurality ofinformation symbols was intended for the first user device 404, whilethe second plurality of information symbols was intended for a differentterminal in the communication network, for instance, user device 406.

The user device 404 then determines a first channel estimate based, atleast in part, on a first sequence of the second plurality of pilotsequences by correlating the second plurality of received symbols withthe first pilot sequence. For instance, user device 404 may determine afirst channel estimate, H₁₁[2], according to

$\begin{matrix}{{H_{11}\lbrack 2\rbrack} = {\sum\limits_{k = 1}^{N_{p}}\left( {{r_{1,k}\lbrack 2\rbrack}{p_{1,k}^{*}\lbrack 2\rbrack}} \right)}} & (18)\end{matrix}$where N_(p) is the number of received pilot symbols, p*_(1,k)[2] is theconjugate of the k^(th) symbol of the first sequence of the secondplurality of pilot sequences, and r_(1,k)[2] is the k^(th) symbol of thesecond plurality of received symbols.

Similarly, the user device 404 determines a second channel estimatebased, at least in part, on a second sequence of the second plurality ofpilot sequences by correlating the second plurality of received symbolswith the second pilot sequence. For instance, user device 404 maydetermine a second channel estimate, H₁₂[2], according to

$\begin{matrix}{{H_{12}\lbrack 2\rbrack} = {\sum\limits_{k = 1}^{N_{p}}\left( {{r_{1,k}\lbrack 2\rbrack}{p_{2,k}^{*}\lbrack 2\rbrack}} \right)}} & (19)\end{matrix}$where N_(p) is the number of received pilot symbols, p*_(2,k)[2] is theconjugate of the le symbol of the second sequence of the secondplurality of pilot sequences, and r_(1,k)[2] is the k^(h) symbol of thesecond plurality of received symbols.

After determining the channel estimates, the user device 404 transmitsthem. They may be transmitted directly to a base station, such as basestation 402, or to an intermediary network location that is incommunication with the base station. One or more composite symbols arethen determined and transmitted to user device 404. The symbols may bedetermined, for example, in accordance with the process described withrespect to the operation of base station 402.

Then, the user device 404 receives one or more composite symbols, whichinclude one or more composite pilot sequences based on the first andsecond plurality of pilot sequences. The pilot sequence may be acombination of the first and second plurality of pilot sequences, forinstance, as shown in equation (9).

The user device 404 may then implement the VDR scheme and determine anestimated effective signal value based on at least one of the compositesymbols. This value may be determined, for instance, using equations(10)-(13) as discussed with respect to base station 402. This mayinclude, for example, determining a third channel estimate based on theone or more composite symbols and forming a plurality of virtual antennareceived symbols. The virtual antenna received symbols are based on thethird channel estimate, the second plurality of received symbols, andthe composite symbols. User device 404 is also able to demodulate thefirst set of data symbols using the first plurality of received symbolsand the estimated effective signal value. The virtual antenna receivedsymbols are estimated effective signal values.

According to particular embodiments, user equipment (UE), such as thedevice diagrammed in FIG. 5, includes one or more antennas 502, one ormore transceivers 504, and data processing resources 506, which togetherare configured to improve data transmission in a communication networkas detailed above.

According to certain embodiments, further constraints regardingorthogonality may be placed on the pilot sequences. For instance, it maybe a requirement that the pilot sequences also be orthogonal acrosstime; i.e., that p₁[1] and p₂[1] are orthogonal to p₁[2] and p₂[2]. Inthis scenario, and given that user device 404 has already computed theestimates Ĥ₁₁[2] and Ĥ₁₂[2], it can now compute the estimate of thechannel tap product H₁₁[3]H₁₁[2], which is given by

$\begin{matrix}{\overset{\_}{{H_{11}\lbrack 3\rbrack}{H_{11}\lbrack 2\rbrack}} = {\sum\limits_{k = 1}^{N_{p}}{{r_{1,k}\lbrack 3\rbrack}{\rho_{1,k}^{*}\lbrack 2\rbrack}}}} & (20)\end{matrix}$Accordingly, there will not be any distortion from the other signalcomponents (see equation 9), since all pilot sequences are orthogonal.Additionally, the product estimate (20) can be divided by Ĥ₁₁[2] toobtain an estimate Ĥ₁₁[3]. Also, as with the result of equation (5) theproduct may be scaled by Σ_(k=1) ^(N) ^(p) p_(j,k)[t]p_(j,k)*[t].

Alternatively, user device 404 can compute the channel tap productestimate H₁₁[3]H₁₂[2] using pilot sequence p₂[2], and divide it byĤ₁₂[2] to obtain another estimate of H₁₁[3].

Also, in order to take advantage of the pilot energy to the largestextent, user device 404 can compute the estimate Ĥ₁₁[3] as an average:

$\begin{matrix}{{{\hat{H}}_{11}\lbrack 3\rbrack} = \frac{{\overset{\_}{{H_{11}\lbrack 3\rbrack}{H_{11}\lbrack 2\rbrack}} \cdot {{\hat{H}}_{12}\lbrack 2\rbrack}} + {\overset{\_}{{H_{11}\lbrack 3\rbrack}{H_{12}\lbrack 2\rbrack}} \cdot {{\hat{H}}_{11}\lbrack 2\rbrack}}}{2 \cdot {{\hat{H}}_{11}\lbrack 2\rbrack} \cdot {{\hat{H}}_{12}\lbrack 2\rbrack}}} & (21)\end{matrix}$Any of the above-identified estimates enables user device 404 tocomplete the VDR transformation.

User device 406 may operate in a similar fashion. For example, at timet=3, it already has Ĥ₂₁[1] and Ĥ₂₂[1], and it can estimate H₁₁[3]H₂₁[1],H₁₁[3]H₂₂[1], or both, and get the corresponding estimate Ĥ₁₁[3].

According to certain embodiments of the present invention, user device404 may determine virtual channel taps. For instance, given that userdevice 404 has the virtual antenna signal r₂ ^(V)[1], for instance, asdetermined with respect to equation (10), it may estimate the virtualchannel tap H₂₁ ^(V)[1]. This may be accomplished by computing the innerproduct with pilot sequence p₁[1]. Similarly, user device 404 may usepilot sequence p₂[1] to estimate H₂₂ ^(V)[1], which enables it tocomplete the VDR. Thus, user device 404 can demodulate the symbolsd_(j,k)[1] using 2-antenna receiver techniques such as minimummean-square error (MMSE) or successive interference cancellation (SIC).User device 406 may operate in a similar way, first estimating the truechannel tap H₂₁[3], then the virtual taps H₁₁ ^(V)[2] and H₁₂ ^(V)[2].

According to particular embodiments, the requirement of orthogonalityacross time may be lifted. In this case, it may be necessary tointroduce an additional sequence p′₁[3], with N_(p) symbols p_(1,k)′[3],that can be placed in the same resource units as previously discussedpilot sequences. The additional sequence should be orthogonal to theother sequences, and equation (9) may be modified as follows:p _(1,k)[3]=H ₁₁[2]p _(1,k)[2]+H ₁₂[2]p _(2,k)[2]+H ₂₁[2]p _(1,k)[1]+H₂₂[2]p _(2,k l[)1]+p _(1,k)′[3]  (22)In this embodiment, the composite pilot sequence is a combination offive pilot sequences. A user device 404, 406 (terminal i) can computethe channel estimate according to

$\begin{matrix}{{{\hat{H}}_{i\; 1}\lbrack 3\rbrack} = {\sum\limits_{k = 1}^{N_{p}}\;{{r_{i,k}\lbrack 3\rbrack}{p_{1,k}^{\prime^{*}}\lbrack 3\rbrack}}}} & (23)\end{matrix}$Again, this value may be scaled, and enables the receiver to completethe VDR transformation.

In certain embodiments, the pilot sequences p₁[1], p₂[1], p₁[2], p₂[2],and p′₁[3] can be based on Walsh-Hadamard sequences or Zadoff-Chusequences. These sequences may all share the same set of radio resourceelements (time, frequency) as illustrated in FIG. 6.

The VDR scheme described above can be generalized to involve more thantwo terminals and more than two transmit antennas. The pilot structurealso generalizes accordingly.

According to certain embodiments of the present invention, the disclosedVDR concept can be applied to a network including transmit antennas ondifferent base stations and multiple user devices. For instance, the VDRconcept may be adapted to a cell-edge scenario, as shown in FIG. 10. Inthis case, different user devices 1006, 1012 may belong to differentbase stations 1002,1008, as shown by their respective cells 1004,1010.Instead of signals from adjacent base stations fighting one another,they can be used constructively. For instance, at time t=1, basestations 1002 and 1008 may simultaneously transmit symbols u₁[1] andu₂[1] respectively, both intended for a first terminal, user device1006. The second terminal, user device 1012, also listens. Similarly, attime t=2, base stations 1002 and 1008 simultaneously transmit symbolsu₁[2] and u₂[2] intended for user device 1012, while user device 1006listens.

In the scenario where each terminal communicates with its own servingbase station, user device 1006 feeds back two channel values H_(1j)[2]to its serving base station 1002 and user device 1012 feeds back twochannel values H_(2j)[1] to its serving base station 1008. It ispresumed that the base stations 1002, 1008 can communicate directly orthrough the infrastructure. After the necessary exchange of information,a composite super-symbol is transmitted simultaneously from both basestations 1002,1008 at time t=3.

The transmission of a common super symbol is possible due to theexchange of information between the base stations and terminals. Forinstance, at a minimum, base station 1002 knows H₁₁[2], H₁₂[2], U₁[1]and u₂[2], while base station 1008 knows H₂₁[1], H₂₂[1], u₂[1] andu₂[2]. In order to synthesize a received value {circumflex over (r)}₁[2]according to equation (6), it is necessary to have H₁₁[2] H₁₂[2], u₁[2]and u₂[2] known by a single device. Therefore, if base station 1008 (ora higher layer in the network) sends u₂[2] to base station 1002, thelatter can construct {circumflex over (r)}₁[2].

Similarly, in order to synthesize {circumflex over (r)}₂[1], it isnecessary to have H₂₁[1], H₂₂[1], u₁[1] and u₂[1] known by a singledevice. If base station 1002 sends u₁[1] to base station 1008, thelatter can construct {circumflex over (r)}₂[1]. Finally, base station1002 can send {circumflex over (r)}₁[2] to base station 1008, and basestation 1008 can send {circumflex over (r)}₂[1] to base station 1002. Attime t=3, both base stations transmit the same combined symbol, forinstance,u ₁[3]=u ₂[3]={circumflex over (r)} ₁[2]+{circumflex over (r)}₂[1]  (24)This transmission may be done in broadcast mode, so that the receivedsignal appears to come from one base station.

The pilot design described above readily applies to the two base stationmodels illustrated in FIGS. 10 and 11. For t=1 and 2, base station itransmit pilot p₁[t]. For t=3, the network uses the channel feedbackvalues received at both base stations to construct and transmit thepilot super-symbol according to equation (9) or (22).

According to certain embodiments, the above-described pilot structureand VDR scheme can be used to further improve performance in acommunication network through the determination of one or more signal tointerference plus noise ratios (SINRs). These SINRs may in turn be: (i)transmitted to a base station, such as base station 402, for subsequentprocessing and use in setting transmission rates; and/or (ii) used todetermine one or more transmission rates at the use device, which arethen transmitted to one or more base stations. These transmission ratesmay be used, for instance, to set the bit rates, in bits per symbol, foreach of the streams u₁[t] and u₂[t].

Referring to FIG. 7, a flow chart 700 is shown, which illustrates aprocess for improving performance in a communication network thatincludes a plurality of transmit antennas and a plurality of userdevices. According to particular embodiments, multiple transmit antennasmay be co-located with a single base station, which is in communicationwith multiple user devices having only a single receive antenna.Alternatively, one or more of the transmit antennas may be co-locatedwith different base stations, for instance, as shown if FIGS. 10 and 11.For example, as shown in FIG. 11, a first transmit antenna could beco-located with base station 1102 while a second antenna is co-locatedwith a second base station 1108. In this example, the communicationnetwork is a heterogeneous network and the second base station 1108 isnot a macrocell base station and is located within a cell 1104 of thefirst base station 1102. One of ordinary skill in the art will recognizethat the following scenarios may be extended to the case of K transmitantennas and K user devices, for K>2. Similarly, the process 700 alsoapplies to user devices that have more than one receive antenna.

In step 702, a user device 404 receives a first set of received symbols.The received symbols may include a first set of data symbols and aplurality of pilot sequences. For instance, the received symbols mayinclude pilot sequence p₁[1] and p₁[2] shown in FIG. 6. They may bereceived from a base station, such as base station 402.

In step 704, the user device 404 receives a second set of receivedsymbols. The second set of received symbols may include a second set ofdata symbols and a second plurality of pilot sequences. For instance,the second set of received symbols may include pilot sequences p₁[2] andp₂[2] shown in FIG. 6. According to particular embodiments, the firstset of received symbols was intended for the user device 404, while thesecond set of received symbols was intended for a different terminal inthe communication network, for instance, user device 406.

In step 706, the user device receives a third set of received symbols.According to particular embodiments, the third set of received symbolsmay be a set of composite symbols, which includes one or more compositepilot sequences based on the first and second plurality of pilotsequences. The composite pilot sequence may be a combination of thefirst and second plurality of pilot sequences, for instance, as shown inequation (9).

In order to determine one or more SINRs in the communication network,and thus, to set transmission rates, the user device must have knowledgeof the average powers on the channels, the associated noise powervalues, the virtual channel power values, and the virtual noise powervalues.

In step 708, the user device obtains a channel noise power value and aset of channel coefficients based on the first set of received symbols.The channel coefficients may be estimated, for instance, based on pilotor reference symbols as described above in conjunction with equation(5). For example, channel coefficients H₁₁[1] and H₁₂[1] may beestimated by correlating the first received symbols with equation (5),wherein the received symbols are of the form:r _(1,k)[1]=H ₁₁[1]p _(1k)[1]+H ₁₂[1]p _(2k)[1]+z _(1k)[1]  (25).This equation is similar to equation (1) discussed above, with theaddition of a symbol index k and use of pilot symbol p rather than datasymbol u. The noise power estimate may also be obtained based onequation (25) and the first received symbols according to:

$\begin{matrix}{p_{z_{1}{\lbrack 1\rbrack}} = {\frac{1}{N_{p}}{\sum\limits_{k = 1}^{N_{p}}\;{{{{r_{1,k}\lbrack 1\rbrack} - {{H_{11}\lbrack 1\rbrack}{p_{1\; k}\lbrack 1\rbrack}} - {{H_{12}\lbrack 1\rbrack}{p_{2\; k}\lbrack 1\rbrack}}}}^{2}.}}}} & (26)\end{matrix}$

According to certain embodiments, the above-identified channel estimatesmay be converted to power estimates, where:P _(H) ₁₁ _([1]) =|H ₁₁[1]|² and P _(H) ₁₂ _([1]) =|H ₁₂[1]|²  (27).Alternatively, the channel estimates may be converted to power estimatesusing time averaging as shown below:

$\begin{matrix}{P_{H_{ij}{\lbrack t\rbrack}} = {\frac{1}{K}{\sum\limits_{k = 0}^{K - 1}\;{{H_{ij}\left\lbrack {t - D - k} \right\rbrack}}^{2}}}} & (28)\end{matrix}$where D is a delay, and K is the number of values. Similarly, thechannel noise power value can be obtained according to:

$\begin{matrix}{P_{z_{i}{\lbrack t\rbrack}} = {\frac{1}{K}{\sum\limits_{k = 0}^{K - 1}\;{{{z_{i}\left\lbrack {t - D - k} \right\rbrack}}^{2}.}}}} & (29)\end{matrix}$

In step 710, the user device obtains a virtual noise channel power valueand a set of virtual channel coefficients. The virtual noise channelpower value and the set of virtual channel coefficients are based on thesecond and third received symbols of steps 704 and 706. These virtualvalues may be determined, for instance, in accordance with theprocedures outlined with respect to equations (1)-(17), which are basedon the pilot structure described herein.

According to certain embodiments, the user device implements VDRprocessing to obtain a virtual receive signal, r₂ ^(V)[1], which isgiven byr ₂ ^(V)[1]=r ₁[3]−H ₁₁[3]r ₁[2]  (30)Thus, the virtual receive signal is determined by the second receivedsymbols, r₁[2], and the third received symbols, r₁[3], and the userdevice must know H₁₁[3]. H₁₁[3] may be determined, for instance, basedon equations (20) and (21) as described above. Once r₂ ^(V)[1] is known,values for the virtual channel coefficients, H^(V) ₂₁[1] and H^(V)₂₂[1], may be obtained by correlating r₂ ^(V)[1] with the appropriatepilot sequences. For example, in a manner similar to that described withrespect to equation (5), r₂ ^(V)[1] may be related to the pilot symbolsaccording tor _(2k) ^(v)[1]=H ₂₁ ^(v)[1]p _(1k)[1]+H ₂₂ ^(v)[1]p _(2k)[1]+z _(2k)^(v)[1]  (31).

Based on the foregoing, estimates for the virtual channel coefficientsH^(v) _(2j)[1], for j=1, 2, can be obtained according to

$\begin{matrix}{H_{2\; j}^{v} = {\frac{1}{N_{p}}{\sum\limits_{k = 1}^{N_{p}}\;{{r_{2\; k}^{v}\lbrack 1\rbrack}{p_{jk}^{*}\lbrack 1\rbrack}}}}} & (32)\end{matrix}$where p*_(j,k)[t] is the conjugate of a pilot signal, p_(j,k)[t],received from a transmit antenna, j, at time t, and N_(p) is a number ofpilot signals.

Similarly, an estimate for the virtual channel noise power can beobtained according to

$\begin{matrix}{P_{z_{2}^{v}{\lbrack 1\rbrack}} = {\frac{1}{N_{p}}{\sum\limits_{k = 1}^{N_{p}}\;{{{{r_{2\; k}^{v}\lbrack 1\rbrack} - {{H_{21}^{v}\lbrack 1\rbrack}{p_{1\; k}\lbrack 1\rbrack}} - {{H_{22}^{v}\lbrack 1\rbrack}{p_{2\; k}\lbrack 1\rbrack}}}}^{2}.}}}} & (33)\end{matrix}$

The virtual channel estimates can be converted to virtual powerestimates according to equations (27) and/or (28). These power estimatesmay then be used in subsequent determinations of SINR.

In step 712, the user device determines a first SINR based on thechannel noise power value, the set of channel coefficients, the virtualchannel noise power value, and the set of virtual channel coefficients.This first SINR, SINR₁[1], indicates the channel conditions for a firstset of information symbols, u₁[1], intended for a first user device att=1. Similarly, a second SINR value, SINR₂[1], is determined for thesecond set of information symbols, u₂[1], intended for a first userdevice at t=1.

The signal to noise plus ratios can be used to determine rates fortransmissions in a subsequent VDR cycle. Thus, according to certainembodiments, SINR₁[1] and SINR₂[1] can be used to determine the rate fortransmissions of the first and second sets of information symbols,respectively, intended for a first user device in a subsequent VDRcycle.

According to certain embodiments, the first signal to interference plusnoise ratio, SINR₁[1], may be determined in accordance with “slow” ratecontrol principles. For instance, SINR₁[1] may be based on one or moreactual channel power to noise ratios and one or more virtual channelpower to noise ratios, utilizing one or more power adjustment factorsassociated with one or more of the transmit antennas. In certainembodiments, a MMSE receiver may be used, in which case SINR₁[1] isdetermined by:

$\begin{matrix}{{{SINR}_{1}\lbrack 1\rbrack} = {\frac{P_{1}P_{H_{11}{\lbrack 1\rbrack}}}{{P_{2}P_{H_{12}{\lbrack 1\rbrack}}} + P_{z_{1}{\lbrack 1\rbrack}}} + \frac{P_{1}P_{H_{21}^{v}{\lbrack 1\rbrack}}}{{P_{2}P_{H_{22}^{v}{\lbrack 1\rbrack}}} + P_{z_{2}^{v}{\lbrack 1\rbrack}}}}} & (34)\end{matrix}$where P₁ is a power adjustment factors associated with a first transmitantenna and P₂ is a power adjustment factor associate with a secondtransmit antenna. P_(H) ₁₁ _([1]) is an average power of a channelbetween the first user device and the first transmit antenna, P_(H) ₁₂_([1]) is an average power of a channel between the first user deviceand a second transmit antenna, and P_(z) ₁ _([i]) is a channel noisepower value. These values may be those obtained in step 708, forinstance, in accordance with equations (25)-(29). P_(z) ₂ _(y) _([1]) isthe virtual channel noise power value obtained in step 710, and P_(H) ₂₁_(v) _([1]) and P_(H) ₂₂ _(v) _([1]) are virtual channel power valuesbased on the set of virtual channel coefficients obtained in step 710.

Applying similar principles, the SINR, SINR₁[2], of a data streamintended for second user device, for instance UE 406, may be given as

$\begin{matrix}{{{SINR}_{1}\lbrack 2\rbrack} = {\frac{P_{1}P_{H_{11}{\lbrack 2\rbrack}}}{{P_{2}P_{H_{12}{\lbrack 2\rbrack}}} + P_{z_{1}{\lbrack 2\rbrack}}} + \frac{P_{1}P_{H_{21}^{v}{\lbrack 2\rbrack}}}{{P_{2}P_{H_{22}^{v}{\lbrack 2\rbrack}}} + P_{z_{2}^{v}{\lbrack 2\rbrack}}}}} & (35)\end{matrix}$when utilizing an MMSE receiver.

According to certain embodiments, the first signal to interference plusnoise ratio, SINR₁[k], for k=1, 2, may be determined in accordance with“fast” rate control principles. In these embodiments, SINR₁[k] isdetermined bySINR₁ [k]=P(H ^(v) ₁ [k])^(H)(P ₂ H ₂ ^(v) [k](H ₂ ^(v) [k])^(H) +R_(z[k]))⁻¹ H ₁ ^(v) [k]  (36)when the device is using an MMSE receiver. H^(v) _(j)[k] is the channelcoefficient vector associated with a device k's virtual MIMO channel,and may be obtained, for instance, as described in step 710. Accordingto certain aspects, H_(j) ^(v)[k] is defined asH _(j) ^(v) [k]=[H _(1j) [k],H _(2j) ^(v) [k]] ^(T)  (37).In equation (36), R_(z[i]) is the noise covariance. According to certainaspects, the noise covariance may be defined byR _(z[k])=diag(σ²,σ² H _(k1)[3])  (38)where σ² is an expectation value of a noise parameter. According toparticular embodiments, the noise covariance may be determined byR _(z[k])=diag(P _(z) ₁ _([1]) ,P _(z) ₂ _(v) _([1]))  (39)wherein P_(z) ₁ _([1]) is a channel noise power value determined inaccordance with step 708 and P_(z) ₂ _(v) _([1]) is a virtual channelnoise power value determined in accordance with step 710.

In step 714, the user device determines a second SINR based on one ormore of the channel noise power value, the set of channel coefficients,the virtual channel noise power value, and the set of virtual channelcoefficients. This second SINR, SINR₂[1], indicates the channelconditions for a second data stream intended for a first user device.

According to certain embodiments, the second signal to interference plusnoise ratio, SINR₂[1] for the first user at t=1, may be determined inaccordance with “slow” rate control principles. For instance, SINR₂[1]may be determined by

$\begin{matrix}{{{SINR}_{2}\lbrack 1\rbrack} = {\frac{P_{2}P_{H_{12}{\lbrack 1\rbrack}}}{{P_{1}P_{H_{11}{\lbrack 1\rbrack}}} + P_{z_{1}{\lbrack 1\rbrack}}} + \frac{P_{2}P_{H_{22}^{v}{\lbrack 1\rbrack}}}{{P_{1}P_{H_{21}^{v}{\lbrack 1\rbrack}}} + P_{z_{2}^{v}{\lbrack 1\rbrack}}}}} & (40)\end{matrix}$when the first user device uses an MMSE receiver. In certainembodiments, it may be advantageous to use a SIC receiver, which cancelsthe interference from the first data stream before detecting the seconddata stream. In this case, the second SINR may be determined by

$\begin{matrix}{{{SINR}_{2}\lbrack 1\rbrack} = {\frac{P_{2}P_{H_{12}{\lbrack 1\rbrack}}}{P_{z_{1}{\lbrack 1\rbrack}}} + {\frac{P_{2}P_{H_{22}^{v}{\lbrack 1\rbrack}}}{P_{z_{2}^{v}{\lbrack 1\rbrack}}}.}}} & (41)\end{matrix}$

Applying similar principles, the second SINR, SINR₂[2], of a second datastream intended for second user device at t=2, for instance UE 406, maybe given as

$\begin{matrix}{{{SINR}_{2}\lbrack 2\rbrack} = {\frac{P_{2}P_{H_{12}{\lbrack 2\rbrack}}}{{P_{1}P_{H_{11}{\lbrack 2\rbrack}}} + P_{z_{1}{\lbrack 2\rbrack}}} + \frac{P_{2}P_{H_{22}^{v}{\lbrack 2\rbrack}}}{{P_{1}P_{H_{21}^{v}{\lbrack 2\rbrack}}} + P_{z_{2}^{v}{\lbrack 2\rbrack}}}}} & (42)\end{matrix}$when the device uses an MMSE receiver, and

$\begin{matrix}{{{SINR}_{2}\lbrack 2\rbrack} = {\frac{P_{2}P_{H_{12}{\lbrack 2\rbrack}}}{P_{z_{1}{\lbrack 2\rbrack}}} + \frac{P_{2}P_{H_{22}^{v}{\lbrack 2\rbrack}}}{P_{z_{2}^{v}{\lbrack 2\rbrack}}}}} & (43)\end{matrix}$when the device uses a SIC receiver.

According to certain embodiments, the second signal to interference plusnoise ratio, SINR₂[k], for k=1,2, may be determined in accordance with“fast” rate control principles. For instance, SINR₂[k] may be determinedbySINR₂ [k]=P ₂(H ₂ ^(v) [k])^(H)(P ₁ H ₁ ^(v) [k](H ₁ ^(v) [k])^(H) +R_(z[k]))⁻¹ H ₂ ^(v) [k]  (44)when the first user device uses an MMSE receiver. In certainembodiments, it may be advantageous to use a SIC receiver, in which casethe second SINR may be determined bySINR₂ [k]=P ₂(H ₂ ^(v) [k])^(H)(R _(z[k]))⁻¹ H ₂ ^(v) [k]  (45).

According to particular embodiments, user equipment (UE), such as thedevice diagrammed in FIG. 5, includes one or more antennas 502, one ormore transceivers 504, and data processing resources 506, which togetherare configured to improve data transmission in a communication networkas in flow chart 700.

As shown in FIG. 9, the SINR values may be used to determinetransmission rates, either at the user device or at a base station. Instep 902, a user device determines first and second signal tointerference plus noise ratios based on a channel noise power value, aset of channel coefficients, a virtual channel noise power value, a theset of virtual channel coefficients describing a communications network.These values and coefficients may be obtained, for instance, asdescribed above with respect to FIG. 7.

In step 904, the SINRs are reported to one or more base stations. Thebase stations can then use the reported values to determine appropriatetransmission rates. Alternatively, or in addition to the reporting ofstep 904, in step 906, the user device may determine one or moretransmission rates based on the SINRs. The transmission rate may bedetermined using a look-up table. For instance, the look-up table ofFIG. 8 illustrates the correlation between SIRN values, modulationorder, and coding rate. According to certain aspects of the embodiment,“transmission rate” may include both modulation and coding rates.However, transmission rates as disclosed herein are not limited to thoseshown in FIG. 8. In step 908, the determined transmission rate istransmitted to one or more base stations.

While various embodiments have been described above, it should beunderstood that they have been presented by way of example only, and notlimitation. Thus, the breadth and scope of the present disclosure shouldnot limited by any of the above-described exemplary embodiments.Moreover, any combination of the above-described elements in allpossible variations thereof is encompassed by the disclosure unlessotherwise indicated herein or otherwise clearly contradicted by context.

Additionally, while the processes described above and illustrated in thedrawings are shown as a sequence of steps, this was done solely for thesake of illustration. Accordingly, it is contemplated that some stepsmay be added, some steps may be omitted, the order of the steps may bere-arranged, and some steps may be performed in parallel.

What is claimed is:
 1. A method for improving performance in acommunication network that includes a plurality of transmit antennas andone or more user devices, comprising: receiving, at a first user device,a first set of received symbols; receiving, at said first user device, asecond set of received symbols; receiving, at said first user device, athird set of received symbols; obtaining a channel noise power value anda set of channel coefficients, wherein said channel noise power valueand said set of channel coefficients are based on said first set ofreceived symbols; obtaining a virtual channel noise power value and aset of virtual channel coefficients, wherein said virtual channel noisepower value and said set of virtual channel coefficients are based onsaid second and third sets of received symbols; determining a firstsignal to interference plus noise ratio based on said channel noisepower value, said set of channel coefficients, said virtual channelnoise power value, and said set of virtual channel coefficients; anddetermining a second signal to interference plus noise ratio based onone or more of said channel noise power value, said set of channelcoefficients, said virtual channel noise power value, and said set ofvirtual channel coefficients, wherein said channel noise power value,said set of channel coefficients, said virtual channel noise powervalue, and said set of virtual channel coefficients are each associatedwith a corresponding one of said plurality of transmit antennas.
 2. Themethod of claim 1, further comprising; reporting said first and secondsignal to interference plus noise ratios to one or more base stations.3. The method of claim 1, further comprising: determining a transmissionrate based on one or more of said first and second signal tointerference plus noise ratios; and transmitting said transmission rateto one or more base stations.
 4. The method of claim 1, wherein said setof channel coefficients, H_(i,j)[t], are determined such that:${{\hat{H}}_{ij}\lbrack t\rbrack} = {\sum\limits_{k = 1}^{N_{p}}\;{{r_{i,k}\lbrack t\rbrack}{p_{j,k}^{*}\lbrack t\rbrack}}}$wherein r_(i,k)[t] is a signal received by a terminal i, at time t,p*_(j,k)[t] is the conjugate of a pilot signal, p_(j,k)[t], receivedfrom one of said plurality of transmit antennas, j, at time t, andN_(p), is a number of pilot signals.
 5. The method of claim 4, whereinsaid channel noise power value, P_(z) ₁ _([1]), is determined such that:$P_{Z_{2}^{U}{\lbrack 1\rbrack}} = {\frac{1}{N_{p}}{\sum\limits_{k = 1}^{N_{p}}{{{{r_{1k}^{v}\lbrack 1\rbrack} - {{H_{11}^{v}\lbrack 1\rbrack}{\lbrack 1\rbrack}} - {{H_{12}^{v}\lbrack 1\rbrack}{p_{2\; k}\lbrack 1\rbrack}}}}^{2}.}}}$6. The method of claim 1, wherein said first signal to interference plusnoise ratio, SINR₁, is determined such that:${{SINR}_{1}\lbrack 1\rbrack} = {\frac{P_{1}P_{H_{11}{\lbrack 1\rbrack}}}{{P_{2}P_{H_{12}{\lbrack 1\rbrack}}} + P_{z_{1}{\lbrack 1\rbrack}}} + \frac{P_{1}P_{H_{21}^{V}{\lbrack 1\rbrack}}}{{P_{2}P_{H_{22}^{V}{\lbrack 1\rbrack}}} + P_{z_{2}^{V}{\lbrack 1\rbrack}}}}$where: P₁ is a power adjustment factor associated with a first of saidplurality of transmit antennas, P₂ is a power adjustment factorassociated with a second of said plurality of transmit antennas, P_(H)₁₁ _([1]) is an average power of a channel between said first userdevice and said first transmit antenna, P_(H) ₁₂ _([1]) is an averagepower of a channel between said first user device and said secondtransmit antenna, P_(z) ₁ _([1]) is said channel noise power value,P_(z) ₂ _(v) _([1]) is said virtual channel noise power value, and P_(H)₂₁ _(V) _([1]) and P_(H) ₁₂ _(V) _([1]) are virtual channel power valuesbased on said set of virtual channel coefficients.
 7. The method ofclaim 6, wherein said first set of received symbols is received on aminimum mean-square error (MMSE) receiver of said first user device, andsaid second signal to interference plus noise ratio, SINR₂, isdetermined such that:${{SINR}_{2}\lbrack 1\rbrack} = {\frac{P_{2}P_{H_{12{\lbrack 1\rbrack}}}}{{P_{1}P_{H_{11}{\lbrack 1\rbrack}}} + P_{z_{1}{\lbrack 1\rbrack}}} + {\frac{P_{2}P_{H_{22}^{V}{\lbrack 1\rbrack}}}{{P_{1}P_{H_{21}^{V}}} + P_{z_{2}^{V}{\lbrack 1\rbrack}}}.}}$8. The method of claim 6, wherein said first set of received symbols isreceived on a successive interference cancellation (SIC) receiver ofsaid first user device, and said second signal to interference plusnoise ratio, SINR₂, is determined such that:${{SINR}_{2}\lbrack 1\rbrack} = {\frac{P_{2}P_{H_{12{\lbrack 1\rbrack}}}}{P_{z_{1}{\lbrack 1\rbrack}}} + {\frac{P_{2}P_{H_{22}^{V}{\lbrack 1\rbrack}}}{P_{z_{2}^{V}{\lbrack 1\rbrack}}}.}}$9. The method of claim 1, wherein said first set of received symbols isreceived from a first of said plurality of transmit antennas and saidsecond set of received symbols is received from a second of saidplurality of transmit antennas.
 10. The method of claim 9, wherein saidfirst and second transmit antennas are co-located with a base station.11. The method of claim 9, wherein said first transmit antenna isco-located with a first base station and said second transmit antenna isco-located with a second base station.
 12. The method of claim 11,wherein said communication network is a heterogeneous network and saidfirst base station is not a macrocell base station and is within a cellof said second base station.
 13. The method of claim 6, wherein P_(H) ₁₁_([1]) is determined such that:P _(H) ₁₁ _([1]) =|H ₁₁[1]|² and P_(H) ₁₂ _([1]) is determined such thatwherein said set of channel coefficients includes coefficients H_(11[)1]and H_(12[)1].
 14. The method of claim 6, wherein P_(H) ₁₁ _([1]) andP_(H) ₁₂ _([1]) are determined such that:$P_{H_{{ij}{\lbrack t\rbrack}}} = {\frac{1}{K}{\sum\limits_{k = 0}^{K - 1}{{H_{ij}\left\lbrack {t - D - k} \right\rbrack}}^{2}}}$over a number of values, k, where H_(ij)[t] indicates one or moretransmission properties between a user device, i, and a transmitantenna, j, and D is a delay.
 15. The method of claim 6, wherein thenoise power estimate P_(z) ₁ _([1]) is determined such that:$P_{z_{i}{\lbrack t\rbrack}} = {\frac{1}{K}{\sum\limits_{k = 0}^{K - 1}{{z_{i}\left\lbrack {t - D - k} \right\rbrack}}^{2}}}$over a number of values, k, where z is a noise value at a terminal, 1,and D is a delay.
 16. The method of claim 1, wherein said first signalto interference plus noise ratio, SINR₁, is determined such that:SINR₁ [k]=P ₁(H ₁ ^(v) [k])^(H)(P ₂ H ₂ ^(v) [k](H ₂ ^(v) [k])^(H) +R_(z[k]))⁻¹ H ₁ ^(v) [k] where: P₁ is a power adjustment factorassociated with a first of said plurality of transmit antennas, P₂ is apower adjustment factor associated with a second of said plurality oftransmit antennas, R_(z[k] is a noise covariance, and) the superscript Hindicates the conjugate transpose, wherein said set of virtual channelcoefficients includes H^(v) ₁[k] and H^(v) ₂[k].
 17. The method of claim16, wherein said noise covariance, R_(z[k]),is determined such that:R _(z[k])=diag(P _(z) ₁ _([1]) ,P _(z) ₂ _(v) _([1])) wherein P_(z) ₁_([1]) is said channel noise power value and P_(z) ₂ _(v) _([1]) is saidvirtual channel noise power value.
 18. The method of claim 16, whereinsaid second set of information symbols is received on a minimummean-square error (MMSE) receiver of said first user device, and saidsecond signal to interference plus noise ratio, SINR₂, is determinedsuch that:SINR₂[1]=P ₂(H ^(v) ₂[1])^(H)(P ₁ H ^(v) ₁[1](H ^(v) ₁[1])^(H) +R_(z[1]))⁻¹ H ^(v) ₂[1].
 19. The method of claim 16, wherein said secondset of information symbols is received on a successive interferencecancellation (SIC) receiver of said first user device, and said secondsignal to interference plus noise ratio, SINR₂, is determined such that:SINR₂[1]=P ₂(H ^(v) ₂[1])^(H) R _(z[1]) ⁻¹ H ^(v) ₂[1].
 20. The methodof claim 1, wherein said set of virtual channel coefficients isdetermined such that:H _(j) ^(v) [k]=[H _(1j) [k],H _(2j) ^(v) [k]] ^(T) wherein H_(ij)[k]represents a channel between a receive terminal, i, and a transmitantenna, j, for a given terminal, k, and H^(v) _(ij)[k] represents avirtual channel between a virtual receive terminal, i, and a transmitantenna, j, for a given terminal, k.
 21. The method of claim 1, whereina portion of said set of virtual channel coefficients, H^(v) _(2j), isdetermined such that:$H_{2j}^{v} = {\frac{1}{N_{p}}{\sum\limits_{k = 1}^{N_{p}}{{r_{2k}^{v}\lbrack 1\rbrack}{p_{jk}^{*}\lbrack 1\rbrack}}}}$wherein r^(v) _(2,k)[t] is a signal received by a terminal i=2, at timet, p*_(j,k)[t] is the conjugate of a pilot signal, p_(j,k)[t], receivedfrom a transmit antenna, j, at time t, and N_(p) is a number of pilotsignals.
 22. The method of claim 21, wherein said virtual channel noisepower value, P_(z) ₂ _(v) [1], is determined such that:$P_{z_{2}^{v}{\lbrack 1\rbrack}} = {\frac{1}{N_{p}}{\sum\limits_{k = 1}^{N_{p}}{{{{r_{2k}^{v}\lbrack 1\rbrack} - {{H_{21}^{v}\lbrack 1\rbrack}{p_{1k}\lbrack 1\rbrack}} - {{H_{22}^{v}\lbrack 1\rbrack}{p_{2k}\lbrack 1\rbrack}}}}^{2}.}}}$23. A mobile device operable in a communication network to receivesignals from a plurality of transmit antennas, comprising: a processor;a memory coupled to the processor; a transceiver coupled to theprocessor; and an antenna coupled to the transceiver configured totransmit and receive signals; wherein the processor is configured to:receive a first set of received symbols; receive a second set ofreceived symbols; receive a third set of received symbols; obtain achannel noise power value and a set of channel coefficients, whereinsaid channel noise power value and said set of channel coefficients arebased on said first set of received symbols; obtain a virtual channelnoise power value and a set of virtual channel coefficients, whereinsaid virtual channel noise power value and said set of virtual channelcoefficients are based on said second and third sets of receivedsymbols; determine a first signal to interference plus noise ratio basedon said channel noise power value, said set of channel coefficients,said virtual channel noise power value, and said set of virtual channelcoefficients; and determine a second signal to interference plus noiseratio based on one or more of said channel noise power value, said setof channel coefficients, said virtual channel noise power value, andsaid set of virtual channel coefficients, wherein said channel noisepower value, said set of channel coefficients, said virtual channelnoise power value, and said set of virtual channel coefficients are eachassociated with a corresponding one of said plurality of transmitantennas.
 24. The device of claim 23, wherein said processor is furtherconfigured to; report said first and second signal to interference plusnoise ratios to one or more base stations.
 25. The device of claim 23,wherein said processor is further configured to: determine atransmission rate based on one or more of said first and second signalto interference plus noise ratios; and transmit said transmission rateto one or more base stations.
 26. The device of claim 23 wherein saidset of channel coefficients, H_(i,j)[t], are determined such that:${{\hat{H}}_{ij}\lbrack t\rbrack} = {\sum\limits_{k = 1}^{N_{p}}{{r_{i,k}\lbrack t\rbrack}{p_{j,k}^{*}\lbrack t\rbrack}}}$wherein r_(i,k)[t] is a signal received by a terminal i, at time t,p*_(j,k)[t] is the conjugate of a pilot signal, p_(j,k)[t], receivedfrom one of said plurality of transmit antennas, j, at time t, and N_(p)is a number of pilot signals.
 27. The device of claim 26, wherein saidchannel noise power value, P_(z) ₁ [1], is determined such that:$p_{z_{2}^{V}{\lbrack 1\rbrack}} = {\frac{1}{N_{p}}{\sum\limits_{k = 1}^{N_{p}}{{{{r_{2k}^{v}\lbrack 1\rbrack} - {{{\hat{H}}_{21}^{v}\lbrack 1\rbrack}{p_{1k}\lbrack 1\rbrack}} - {{{\hat{H}}_{22}^{v}\lbrack 1\rbrack}{p_{2k}\lbrack 1\rbrack}}}}^{2}.}}}$28. The device of claim 23, wherein said first signal to interferenceplus noise ratio, SINR₁, is determined such that:${{SINR}_{1}\lbrack 1\rbrack} = {\frac{P_{1}P_{H_{11}{\lbrack 1\rbrack}}}{{P_{2}P_{H_{12}{\lbrack 1\rbrack}}} + P_{z_{1}{\lbrack 1\rbrack}}} + \frac{P_{1}P_{H_{21}^{V}{\lbrack 1\rbrack}}}{{P_{2}P_{H_{22}^{V}}} + P_{z_{2}^{V}{\lbrack 1\rbrack}}}}$where: P₁ is a power adjustment factor associated with a first of saidplurality of transmit antennas, P₂ is a power adjustment factorassociated with a second of said plurality of transmit antennas, P_(H)₁₁ _([1]) is an average power of a channel between the device and saidfirst transmit antenna, P_(H) ₁₂ _([1]) is an average power of a channelbetween the device and said second transmit antenna, P_(z) ₁ _([1]) issaid channel noise power value, P_(z) ₂ _(v) _([1]) is said virtualchannel noise power value, and P_(H) ₂₁ _(v) _([1]) and P_(H) ₂₂ _(v)_([1]) are virtual channel power values based on said set of virtualchannel coefficients.
 29. The device of claim 28, wherein saidtransceiver is configured as a minimum mean-square error (MMSE) receiverand said second signal to interference plus noise ratio, SINR₂, isdetermined such that:${{SINR}_{2}\lbrack 1\rbrack} = {\frac{P_{2}P_{H_{12{\lbrack 1\rbrack}}}}{{P_{1}P_{H_{11}{\lbrack 1\rbrack}}} + P_{z_{1}{\lbrack 1\rbrack}}} + {\frac{P_{2}P_{H_{22}^{V}{\lbrack 1\rbrack}}}{{P_{1}P_{H_{21}^{V}}} + P_{z_{2}^{V}{\lbrack 1\rbrack}}}.}}$30. The device of claim 28, wherein said transceiver is configured is asuccessive interference cancellation (SIC) receiver and said secondsignal to interference plus noise ratio, SINR₂, is determined such that:${{SINR}_{2}\lbrack 1\rbrack} = {\frac{P_{2}P_{H_{12}{\lbrack 1\rbrack}}}{P_{z_{1}{\lbrack 1\rbrack}}} + {\frac{P_{2}P_{H_{22}^{V}{\lbrack 1\rbrack}}}{P_{z_{2}^{V}{\lbrack 1\rbrack}}}.}}$31. The device of claim 23, wherein said first set of received symbolsis received from a first of said plurality of transmit antennas and saidsecond set of received symbols is received from a second of saidplurality of transmit antennas.
 32. The device of claim 31, wherein saidfirst and second transmit antennas are co-located with a base station.33. The device of claim 31, wherein said first transmit antenna isco-located with a first base station and said second transmit antenna isco-located with a second base station.
 34. The device of claim 33,wherein said communication network is a heterogeneous network and saidfirst base station is not a macrocell base station and is within a cellof said second base station.
 35. The device of claim 28, wherein P_(H)₁₁ _([1]) determined such that:P _(H) ₁₁ _([1]) =|H ₁₁[1]|² and P_(H) ₁₂ _([1]) is determined suchthat:P _(H) ₁₂ _([1]) =|H ₁₂[1]|² wherein said set of channel coefficientsincludes coefficients H₁₁[1] and H₁₂[1].
 36. The device of claim 28,wherein P_(H) ₁₁ _([1]) and P_(H) ₁₂ _([1]) are determined such that:$P_{H_{ij}{\lbrack 1\rbrack}} = {\frac{1}{K}{\sum\limits_{k = 0}^{K - 1}{{H_{ij}\left\lbrack {t - D - k} \right\rbrack}}^{2}}}$over a number of values, k, where H_(ij)[t] indicates one or moretransmission properties between a user device, i, and a transmitantenna, j, and D is a delay.
 37. The device of claim 28, wherein thenoise power estimate P_(z) ₁ _([1]) is determined such that:$P_{z_{i}{\lbrack t\rbrack}} = {\frac{1}{K}{\sum\limits_{k = 0}^{K - 1}{{z_{i}\left\lbrack {t - D - k} \right\rbrack}}^{2}}}$over a number of values, k, where z_(i) is a noise value at a terminal,i, and D is a delay.
 38. The device of claim 23, wherein said firstsignal to interference plus noise ratio, SINR₁, is determined such that:SINR₁ [k]=P ₁(H ₁ ^(v) [k])^(H)(P ₂ H ₂ ^(v) [k](H ₂ ^(v) [k])^(H) +R_(z[k])) ⁻¹ H ₁ ^(v) [k] where: P₁ is a power adjustment factorassociated with a first of said plurality of transmit antennas, P₂ is apower adjustment factor associated with a second of said plurality oftransmit antennas, R_(z[k]) is a noise covariance, and the superscript Hindicates the conjugate transpose, wherein said set of virtual channelcoefficients includes H^(v) ₁[k] and H^(v) ₂[k].
 39. The device of claim38, wherein said noise covariance, R_(z[k]), is determined such that:R _(z[k])=diag(P _(z) ₁ _([1]) ,P _(z) ₂ _(v) _([1])) Wherein P_(z) ₁_([1]) is said channel noise power value and P_(z) ₂ _(v) _([1]) is saidvirtual channel noise power value.
 40. The device of claim 38, whereinsaid transceiver is configured as a minimum mean-square error (MMSE)receiver and said second signal to interference plus noise ratio, SINR₂,is determined such that:SINR₂[1]=P ₂(H ^(v) ₂[1])^(H)(P ₁ H ^(v) ₁[1](H ^(v) ₁[1])^(H) +R_(z[1])) ⁻¹ H ^(v) ₂[1].
 41. The device of claim 38, wherein saidtransceiver is configured as a successive interference cancellation(SIC) receiver and said second signal to interference plus noise ratio,SINR₂, is determined such that:SINR₂[1]=P ₂(H ^(v) ₂[1])^(H) R _(z[1]) ⁻¹ H ^(v) ₂[1].
 42. The deviceof claim 23, wherein said set of virtual channel coefficients isdetermined such that:H _(j) ^(v) [k]=[H _(1j) ,[k],H _(2j) ^(v) [k]] ^(T) wherein H_(ij)[k]represents a channel between a receive terminal, i, and a transmitantenna, j, for a given terminal, k, and H^(v) _(ij)[k] represents avirtual channel between a virtual receive terminal, i, and a transmitantenna, j, for a given terminal, k.
 43. The device of claim 23, whereina portion of said set of virtual channel coefficients, H^(v) _(2j), isdetermined such that:$H_{2j}^{v} = {\frac{1}{N_{p}}{\sum\limits_{k = 1}^{N_{p}}{{r_{2k}^{v}\lbrack 1\rbrack}{p_{jk}^{*}\lbrack 1\rbrack}}}}$wherein r^(v) _(2,k)[t] is a signal received by a terminal i=2, at timet, p*_(j,k)[t] is the conjugate of a pilot signal, p_(j,k)[t], receivedfrom a transmit antenna, j, at time t, and N_(p) is a number of pilotsignals.
 44. The device of claim 43, wherein said virtual channel noisepower value, P_(z) ₂ _(V) _([1]), is determined such that:$P_{z_{2}^{v}{\lbrack 1\rbrack}} = {\frac{1}{N_{p}}{\sum\limits_{k = 1}^{N_{p}}{{{{r_{2k}^{v}\lbrack 1\rbrack} - {{H_{21}^{v}\lbrack 1\rbrack}{p_{1k}\lbrack 1\rbrack}} - {{H_{22}^{v}\lbrack 1\rbrack}{p_{2k}\lbrack 1\rbrack}}}}^{2}.}}}$